MAKING NYLON:http://www.bcscience.com/bc10/pgs/videos_012_making_nylon.html

1. Explain how factors such as temperature, concentration, the presence of a catalyst, and surface area can speed up or slow down the rate of chemical reactions.

Endothermic

Exothermic

Energy of Activation

Reaction Rate

Catalyst

Concentration

Surface Area

Temperature

Collision theory

1. Energy is involved in every chemical reaction.

All chemical reactions require two steps:

a)the atoms of the reactants are broken apartb) the atoms of the reactants recombine to form

products

e.g. magnesium + sulphuric acid ==> magnesium sulphate + hydrogen

Mg(s) + H2SO4(aq) ==> MgSO4(aq) + H2(g)

Chemical bonds hold atoms together.

In chemical reactions, you need energy to break apart the bonds that hold the atoms of the reactants together.

Ie:

When products are formed, energy is also released.

• Sometimes MORE energy is ABSORBED or used up for a reaction to occur

Endothermic Reactions must absorb heat to occur, and usually get cold as a result.

•Ammonium thiocyanate is mixed with barium hydroxide.

•A slush forms.

•A drop of water is placed on a block of wood.

•The reaction is endothermic, that is, it takes in heat.

•As a result, the bottom of the beaker becomes cold enough to freeze the water and stick to the wood.

http://www.youtube.com/watch?v=5RJLvQXce4A&feature=channel

• Sometimes MORE energy is RELEASED or given off when a reaction occurs

Exothermic Reactions will release heat when they occur, and usually get warm or hot as a result.

1. Sodium peroxide (yellow powder) added to zinc powder (gray powder).

2. Water is squirted in; the mixture ignites

3. Violent, strong exothermic reaction 4. Zinc powder keeps burning.

•Thermic lancing is a hot cutting process, using an exothermic reaction to generate temperatures in excess of 3000 deg C.

•The lance is consumed, melting both concrete and steel.

•Used for cutting heavily reinforced concrete and steel sections.

•Ie: steel bridge deck removal

If the energy absorbed to break apart the atoms in the reactants is GREATER THANGREATER THAN the energy released to form the products, the reaction is ENDOTHERMICENDOTHERMIC (it absorbs energy from its surroundings).

If the energy absorbed to break apart the atoms in the reactants is LESS THANLESS THAN the energy released to form the products, the reaction is EXOTHERMICEXOTHERMIC (it releases energy into its surroundings).

Potassium permanganate and glycerin:http://www.youtube.com/watch?v=nEeSgyuCBl8&feature=related

2. Chemical reactions take place at different rates (speeds).

‘Rate of reaction’ means 'the speed of the reaction'.

•If a reaction is SLOW, that means the molecules combine at a slower speed than a fast reaction.

•Some reactions take hundreds, maybe even thousands of years while others can happen in less than one second.

Rusting is a ‘slow’ reaction, you hardly see any change looking at it!

The weathering of rocks is a very slow reaction.

An example of a fast reaction would be mixing sodium and water to form sodium hydroxide.

Explosions and burning/combustion reactions would be described as ‘very fast’!

The collision theory says that when more collisions occur between the reactants, there is a better chance that products will be made.

So, more collisions = products form faster. This would be a fast reaction rate.

What do you think scientists like you could do to increase the rate of reaction?

How can we increase the # of collisions that occur between reactants?

Rates of reaction are affected by four things:

a) Temperature

b) Surface area of solid reactants

c) Concentration of liquid reactants

d) Catalysts

•When you INCREASE the temperature, the molecules bounce around a lot more (because they have more energy).

•When they bounce around more, they are more likely to COLLIDE.

•Therefore, they are more likely to combine into PRODUCTS.

•So increased temperature = increased RATE of reaction.

Sometimes we want slower reactions (we use a fridge to prevent spoilage).

Sometimes we want faster reactions (we cook food to speed up the production of new molecules).

Concentration refers to how many molecules of a substance exist in a certain amount of liquid.

Concentration is how much solute is dissolved in solution.

It is measured in grams/litre. Changing the concentration of O2 changes the intensity

of flames.

•If there are more reactants available, there is a greater chance that the molecules will collide.

•Therefore, there is a greater chance of products forming more quickly.

•Increased concentration = increased rate of the reaction.

•You are only going to get a reaction if the particles collide with each other.

•Increasing the surface area of the solid increases the chances of a collision taking place.

Sometimes, increasing the temperature or concentration is not a desirable method to increase reaction rate… it may be impractical or dangerous.

A catalyst is a chemical that speeds up the reaction rate, but doesn’t get used up as a reactant. It can do its job over and over again.

An enzyme is an example of a biological catalyst. (ie: salivary amylase)

A catalyst decreases the amount of energy that is required to break the bonds between the reactants so that products can form.

EXAMPLE: Catalytic converters

Catalytic converters use metals like platinum, palladium and rhodium to convert poisonous compounds in vehicle exhausts into less harmful things.

THIS = LESS POLLUTION!

Catalysts in the honeycomb-shaped filters in the converter help to change many of the pollutants into less harmful substances.

1. Poisonous carbon monoxide is changed into CO2.

2. Hydrocarbons are converted into CO2 and H2O.

3. Nitrogen oxides are changed into N2 and O2.2N2O3 2N2 + 3O2

1.Add a catalyst to speed up the reaction

2. Increase the temperature

3. Increase the surface area (break solid into smaller pieces)

4. Increase the concentration of the liquid (put more solute in the water)

1. Decrease the temperature where the reaction occurs.

2. Decrease the concentration of reactants.

3. Decrease the amount of surface area that reacts.

4. Remove a catalyst or add an inhibitor.